The operation of a room air conditioner in areas where the outside temperature is high, can result in discharge pressures for the compressor which become elevated to a level whereby the compressor becomes overloaded and fails to operate properly. Normally, under such conditions, an automatic overload switch will deenergize the compressor to prevent it from becoming damaged due to overloading. This, of course, will result in a complete loss in cooling capacity of the air conditioner.
In order to maintain some cooling capacity under such conditions, some large compressor units have been fitted with a control device which, in effect, reduces the capacity of the compressor to reduce the load on the compressor. Practical considerations preclude the use of such devices on the smaller compressors found in "room-type" air conditioners.
Another method, which has been employed to maintain some cooling capacity under heavy loads while reducing the danger of damage to the compressor, or its "shut-down" as a result of overloading, is the use of an automatic expansion valve to throttle the refrigerant flow to all of the evaporator coil circuits. This device, in response to increasing pressure in the system, reduces the flow of refrigerant to the evaporator coil circuits and thereby effectively reduces the load on the compressor.
There is a loss in the efficiency of the air conditioner unit inherent in both of the above systems, but some cooling capacity is maintained.